System for accessing subterranean deposits from the surface

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 09/444,029, filed Nov. 19, 1999, by Joseph A. Zupanick entitled “Method and System for Accessing Subterranean Deposits from the Surface, now U.S. Pat. No. 6,357,523 which is a continuation-in-part of U.S. application Ser. No. 09/197,687, filed Nov. 20, 1998, by Joseph A. Zupanick entitled “Method for Production of Gas from a Coal Seam” now U.S. Pat. No. 6,280,000.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the recovery of subterranean deposits, and more particularly to a method and system for accessing subterranean deposits from the surface.

BACKGROUND OF THE INVENTION

Subterranean deposits of coal contain substantial quantities of entrained methane gas limited in production in use of methane gas from coal deposits has occurred for many years. Substantial obstacles, however, have frustrated more extensive development and use of methane gas deposits in coal seams. The foremost problem in producing methane gas from coal seams is that while coal seams may extend over large areas of up to several thousand acres, the coal seams are fairly shallow in depth, varying from a few inches to several meters. Thus, while the coal seams are often relatively near the surface, vertical wells drilled into the coal deposits for obtaining methane gas can only drain a fairly small radius around the coal deposits. Further, coal deposits are not amendable to pressure fracturing and other methods often used for increasing methane gas production from rock formations. As a result, once the gas easily drained from a vertical well bore in a coal seam is produced, further production is limited in volume. Additionally, coal seams are often associated with subterranean water, which must be drained from the coal seam in order to produce the methane.

Horizontal drilling patterns have been tried in order to extend the amount of coal seams exposed to a drill bore for gas extraction. Such horizontal drilling techniques, however, require the use of a radiused well bore which presents difficulties in removing the entrained water from the coal seam. The most efficient method for pumping water from a subterranean well, a sucker rod pump, does not work well in horizontal or radiused bores.

A further problem for surface production of gas from coal seams is the difficulty presented by under balanced drilling conditions caused by the porousness of the coal seam. During both vertical and horizontal surface drilling operations, drilling fluid is used to remove cuttings from the well bore to the surface. The drilling fluid exerts a hydrostatic pressure on the formation which, if it exceeds the hydrostatic pressure of the formation, can result in a loss of drilling fluid into the formation. This results in entrainment of drilling finds in the formation, which tends to plug the pores, cracks, and fractures that are needed to produce the gas.

As a result of these difficulties in surface production of methane gas from coal deposits, the methane gas which must be removed from a coal seam prior to mining, has been removed from coal seams through the use of subterranean methods. While the use of subterranean methods allows water to be easily removed from a coal seam and eliminates under balanced drilling conditions, they can only access a limited amount of the coal seams exposed by current mining operations. Where longwall mining is practiced, for example, underground drilling rigs are used to drill horizontal holes from a panel currently being mined into an adjacent panel that will later be mined. The limitations of underground rigs limits the reach of such horizontal holes and thus the area that can be effectively drained. In addition, the degasification of a next panel during mining of a current panel limits the time for degasification. As a result, many horizontal bores must be drilled to remove the gas in a limited period of time. Furthermore, in conditions of high gas content or migration of gas through a coal seam, mining may need to be halted or delayed until a next panel can be adequately degasified.

These production delays add to the expense associated with degasifying a coal seam.

SUMMARY OF THE INVENTION

The present invention provides an improved method and system for accessing subterranean deposits from the surface that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods. In particular, the present invention provides an articulated well with a drainage pattern that intersects a horizontal cavity well. The drainage patterns provide access to a large subterranean area from the surface while the vertical cavity well allows entrained water, hydrocarbons, and other deposits to be efficiently removed and/or produced.

In accordance with one embodiment of the present invention, a method for accessing a subterranean zone from the surface includes drilling a substantially vertical well bore from the surface to the subterranean zone. An articulated well bore is drilled from the surface to the subterranean zone. The articulated well bore is horizontally offset from the substantially vertical well bore at the surface and intersects the substantially vertical well bore at a junction proximate to the subterranean zone. A substantially horizontal drainage pattern is drilled through the articulated well bore from the junction into the subterranean zone.

In accordance with another aspect of the present invention, the substantially horizontal drainage pattern may comprise a pinnate pattern including a substantially horizontal diagonal well bore extending from the substantially vertical well bore that defines a first end of an area covered by the drainage pattern to a distant end of the area. A first of substantially horizontal lateral well bores extend in space relation to each other from the diagonal well bore to the periphery of the area on a first side of the diagonal well bore. A second set of substantially horizontal lateral well bores extend in space relation to each other from the diagonal well bore to the periphery of the area on a second, opposite side of the diagonal.

In accordance with still another aspect of the present invention, a method for preparing a subterranean zone for mining uses the substantially vertical and articulated well bores and the drainage pattern. Water is drained from the subterranean zone through the drainage pattern to the junction of the substantially vertical well bore. Water is pumped from the junction to the surface through the substantially vertical well bore. Gas is produced from the subterranean zone through at least one of the substantially vertical and articulated well bores. After degasification has been completed, the subterranean zone may be further prepared by pumping water and other additives into the zone through the drainage pattern.

In accordance with yet another aspect of the present invention, a pump positioning device is provided to accurately position a downhole pump in a cavity of a well bore.

Technical advantages of the present invention include providing an improved method and system for accessing subterranean deposits from the surface. In particular, a horizontal drainage pattern is drilled in a target zone from an articulated surface well to provide access to the zone from the surface. The drainage pattern intersected by a vertical cavity well from which entrained water, hydrocarbons, and other fluids drained from the zone can be efficiently removed and/or produced by a rod pumping unit. As a result, gas, oil, and other fluids can be efficiently produced at the surface from a low pressure or low porosity formation.

Another technical advantage of the present invention includes providing an improved method and system for drilling into low-pressure reservoirs. In particular, a downhole pump or gas lift is used to lighten hydrostatic pressure exerted by drilling fluids used to remove cuttings during drilling operations. As a result, reservoirs may be drilled at ultra-low pressures without loss of drilling fluids into the formation and plugging of the formation.

Yet another technical advantage of the present invention includes providing an improved horizontal drainage pattern for accessing a subterranean zone. In particular, a pinnate structure with a main diagonal and opposed laterals is used to maximize access to a subterranean zone from a single vertical well bore. Length of the laterals is maximized proximate to the vertical well bore and decreased toward the end of the main diagonal to provide uniform access to a quadrilateral or other grid area. This allows the drainage pattern to be aligned with longwall panels and other subsurface structures for degasification of a mine coal seam or other deposit.

Still another technical advantage of the present invention includes providing an improved method and system for preparing a coal seam or other subterranean deposit for mining. In particular, surface wells are used to degasify a coal seam ahead of mining operations. This reduces underground equipment and activities and increases the time provided to degasify the seam which minimizes shutdowns due to high gas content. In addition, water and additives may be pumped into the degasified coal seam prior to mining operations to minimize dust and other hazardous conditions, to improve efficiency of the mining process, and to improve the quality of the coal product.

Still another technical advantage of the present invention includes providing an improved method and system for producing methane gas from a mined coal seam. In particular, well bores used to initially degasify a coal seam prior to mining operations may be reused to collect gob gas from the seam after mining operation. As a result, costs associated with the collection of gob gas are minimized to facilitate or make feasible the collection of gob gas from previously mined seams.

Still another technical advantage of the present invention includes providing a positioning device for automatically positioning down-hole pumps and other equipment in a cavity. In particular, a rotatable cavity positioning device is configured to retract for transport in a well bore and to extend within a down-hole cavity to optimally position the equipment within the cavity. This allows down-hole equipment to be easily positioned and secured within the cavity.

Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, wherein like numerals represent like parts, in which:

FIG. 1 is a cross-sectional diagram illustrating formation of a horizontal drainage pattern in a subterranean zone through an articulated surface well intersecting a vertical cavity well in accordance with one embodiment of the present invention;

FIG. 2 is a cross-sectional diagram illustrating formation of the horizontal drainage pattern in the subterranean zone through the articulated surface well intersecting the vertical cavity well in accordance with another embodiment of the present invention;

FIG. 3 is a cross-sectional diagram illustrating production of fluids from a horizontal draining pattern in a subterranean zone through a vertical well bore in accordance with one embodiment of the present invention;

FIG. 4 is a top plan diagram illustrating a pinnate drainage pattern for accessing deposits in a subterranean zone in accordance with one embodiment of the present invention;

FIG. 5 is a top plan diagram illustrating a pinnate drainage pattern for accessing deposits in a subterranean zone in accordance with another embodiment of the present invention;

FIG. 6 is a top plan diagram illustrating a quadrilateral pinnate drainage pattern for accessing deposits in a subterranean zone in accordance with still another embodiment of the present invention;

FIG. 7 is a top plan diagram illustrating the alignment of pinnate drainage patterns within panels of a coal seam for degasifying and preparing the coal seam for mining operations in accordance with one embodiment of the present invention; and

FIG. 8 is a flow diagram illustrating a method for preparing a coal seam for mining operations in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a cavity and articulated well combination for accessing a subterranean zone from the surface in accordance with one embodiment of the present invention. In this embodiment, the subterranean zone is a coal seam. It will be understood that other low pressure, ultra-low pressure, and low porosity subterranean zones can be similarly accessed using the dual well system of the present invention to remove and/or produce water, hydrocarbons and other fluids in the zone and to treat minerals in the zone prior to mining operations.

Referring to FIG. 1, a substantially vertical well bore <b>12</b> extends from the surface <b>14</b> to a target coal seam <b>15</b>. The substantially vertical well bore <b>12</b> intersects, penetrates and continues below the coal seam <b>15</b>. The substantially vertical well bore is lined with a suitable well casing <b>16</b> that terminates at or above the level of the coal seam <b>15</b>.

The substantially vertical well bore <b>12</b> is logged either during or after drilling in order to locate the exact vertical depth of the coal seam <b>15</b>. As a result, the coal seam is not missed in subsequent drilling operations and techniques used to locate the seam <b>15</b> while drilling need not be employed. An enlarged diameter cavity <b>20</b> is formed in the substantially vertical well bore <b>12</b> at the level of the coal seam <b>15</b>. As described in more detail below, the enlarged diameter cavity <b>20</b> provides a junction for intersection of the substantially vertical well bore by articulated well bore used to form a substantially horizontal drainage pattern in the coal seam <b>15</b>. The enlarged diameter cavity <b>20</b> also provides a collection point for fluids drained from the coal seam <b>15</b> during production operations.

In one embodiment, the enlarged diameter cavity <b>20</b> has a radius of approximately eight feet and a vertical dimension which equals or exceeds the vertical dimension of the coal seam <b>15</b>. The enlarged diameter cavity <b>20</b> is formed using suitable under-reaming techniques and equipment. A vertical portion of the substantially vertical well bore <b>12</b> continues below the enlarged diameter cavity <b>20</b> to form a sump <b>22</b> for the cavity <b>20</b>.

An articulated well bore <b>30</b> extends from the surface <b>14</b> to the enlarged diameter cavity <b>20</b> of the substantially vertical well bore <b>12</b>. The articulated well bore <b>30</b> includes a substantially vertical portion <b>32</b>, a substantially horizontal portion <b>34</b>, and a curved or radiused portion <b>36</b> interconnecting the vertical and horizontal portions <b>32</b> and <b>34</b>. The horizontal portion <b>34</b> lies substantially in the horizontal plane of the coal seam <b>15</b> and intersects the large diameter cavity <b>20</b> of the substantially vertical well bore <b>12</b>.

The articulated well bore <b>30</b> is offset a sufficient distance from the substantially vertical well bore <b>12</b> at the surface <b>14</b> to permit the large radius curved section <b>36</b> and any desired horizontal section <b>34</b> to be drilled before intersecting the enlarged diameter cavity <b>20</b>. To provide the curved portion <b>36</b> with a radius of 100-150 feet, the articulated well bore <b>30</b> is offset a distance of about 300 feet from the substantially vertical well bore <b>12</b>. This spacing minimizes the angle of the curved portion <b>36</b> to reduce friction in the bore <b>30</b> during drilling operations. As a result, reach of the articulated drill string drilled through the articulated well bore <b>30</b> is maximized.

The articulated well bore <b>30</b> is drilled using articulated drill string <b>40</b> that includes a suitable down-hole motor and bit <b>42</b>. A measurement while drilling (MWD) device <b>44</b> is included in the articulated drill string <b>40</b> for controlling the orientation and direction of the well bore drilled by the motor and bit <b>42</b>. The substantially vertical portion <b>32</b> of the articulated well bore <b>30</b> is lined with a suitable casing <b>38</b>.

After the enlarged diameter cavity <b>20</b> has been successfully intersected by the articulated well bore <b>30</b>, drilling is continued through the cavity <b>20</b> using the articulated drill string <b>40</b> and appropriate horizontal drilling apparatus to provide a substantially horizontal drainage pattern <b>50</b> in the coal seam <b>15</b>. The substantially horizontal drainage pattern <b>50</b> and other such well bores include sloped, undulating, or other inclinations of the coal seam <b>15</b> or other subterranean zone. During this operation, gamma ray logging tools and conventional measurement while drilling devices may be employed to control and direct the orientation of the drill bit to retain the drainage pattern <b>50</b> within the confines of the coal seam <b>15</b> and to provide substantially uniform coverage of a desired area within the coal seam <b>15</b>. Further information regarding the drainage pattern is described in more detail below in connection with FIGS. 4-7.

During the process of drilling the drainage pattern <b>50</b>, drilling fluid or “mud” is pumped down the articulated drill string <b>40</b> and circulated out of the drill string <b>40</b> in the vicinity of the bit <b>42</b>, where it is used to scour the formation and to remove formation cuttings. The cuttings are then entrained in the drilling fluid which circulates up through the annulus between the drill string <b>40</b> and the well bore walls until it reaches the surface <b>14</b>, where the cuttings are removed from the drilling fluid and the fluid is then recirculated. This conventional drilling operation produces a standard column of drilling fluid having a vertical height equal to the depth of the well bore <b>30</b> and produces a hydrostatic pressure on the well bore corresponding to the well bore depth. Because coal seams tend to be porous and fractured, they may be unable to sustain such hydrostatic pressure, even if formation water is also present in the coal seam <b>15</b>. Accordingly, if the full hydrostatic pressure is allowed to act on the coal seam <b>15</b>, the result may be loss of drilling fluid and entrained cuttings into the formation. Such a circumstance is referred to as an “over balanced” drilling operation in which the hydrostatic fluid pressure in the well bore exceeds the ability of the formation to withstand the pressure. Loss of drilling fluids in cuttings into the formation not only is expensive in terms of the lost drilling fluids, which must be made up, but it tends to plug the pores in the coal seam <b>15</b>, which are needed to drain the coal seam of gas and water.

To prevent over balance drilling conditions during formation of the drainage pattern <b>50</b>, air compressors <b>60</b> are provided to circulate compressed air down the substantially vertical well bore <b>12</b> and back up through the articulated well bore <b>30</b>. The circulated air will admix with the drilling fluids in the annulus around the articulated drill string <b>40</b> and create bubbles throughout the column of drilling fluid. This has the effective of lightening the hydrostatic pressure of the drilling fluid and reducing the down-hole pressure sufficiently that drilling conditions do not become over balanced. Aeration of the drilling fluid reduces down-hole pressure to approximately 150-200 pounds per square inch (psi). Accordingly, low pressure coal seams and other subterranean zones can be drilling without substantial loss of drilling fluid and contamination of the zone by the drilling fluid.

Foam, which may be compressed air mixed with water, may also be circulated down through the articulated drill string <b>40</b> along with the drilling mud in order to aerate the drilling fluid in the annulus as the articulated well bore <b>30</b> is being drilled and, if desired, as the drainage pattern <b>50</b> is being drilled. Drilling of the drainage pattern <b>50</b> with the use of an air hammer bit or an air-powered down-hole motor will also supply compressed air or foam to the drilling fluid. In this case, the compressed air or foam which is used to power the bit or down-hole motor exits the vicinity of the drill bit <b>42</b>. However, the larger volume of air which can be circulated down the substantially vertical well bore <b>12</b>, permits greater aeration of the drilling fluid than generally is possible by air supplied through the articulated drill string <b>40</b>.

FIG. 2 illustrates method and system for drilling the drainage pattern <b>50</b> in the coal seam <b>15</b> in accordance with another embodiment of the present invention. In this embodiment, the substantially vertical well bore <b>12</b>, enlarged diameter cavity <b>20</b> and articulated well bore <b>32</b> are positioned and formed as previously described in connection with the FIG. <b>1</b>.

Referring to FIG. 2, after intersection of the enlarged diameter cavity <b>20</b> by the articulated well bore <b>30</b> a pump <b>52</b> is installed in the enlarged diameter cavity <b>20</b> to pump drilling fluid and cuttings to the surface <b>14</b> through the substantially vertical well bore <b>12</b>. This eliminates the friction of air and fluid returning up the articulated well bore <b>30</b> and reduces down-hole pressure to nearly zero. Accordingly, coal seams and other subterranean zones having ultra low pressures below 150 psi can be accessed from the surface. Additionally, the risk of combining air and methane in the well is eliminated.

FIG. 3 illustrates production of fluids from the horizontal drainage pattern <b>50</b> in the coal seam <b>15</b> in accordance with one embodiment of the present invention. In this embodiment, after the substantially vertical and articulated well bores <b>12</b> and <b>30</b> as well as desired drainage pattern <b>50</b> have been drilled, the articulated drill string <b>40</b> is removed from the articulated well bore <b>30</b> and the articulated well bore is capped. For multiple pinnate structure described below, the articulated well <b>30</b> may be plugged in the substantially horizontal portion <b>34</b>. Otherwise, the articulated well <b>30</b> may be left unplugged.

Referring to FIG. 3, a down hole pump <b>80</b> is disposed in the substantially vertical well bore <b>12</b> in the enlarged diameter cavity <b>22</b>. The enlarged cavity <b>20</b> provides a reservoir for accumulated fluids allowing intermittent pumping without adverse effects of a hydrostatic head caused by accumulated fluids in the well bore.

The down hole pump <b>140</b> is connected to the surface <b>14</b> via a tubing string <b>82</b> and may be powered by sucker rods <b>84</b> extending down through the well bore <b>12</b> of the tubing. The sucker rods <b>84</b> are reciprocated by a suitable surface mounted apparatus, such as a powered walking beam <b>86</b> to operate the down hole pump <b>80</b>. The down hole pump <b>80</b> is used to remove water and entrained coal fines from the coal seam <b>15</b> via the drainage pattern <b>50</b>. Once the water is removed to the surface, it may be treated for separation of methane which may be dissolved in the water and for removal of entrained fines. After sufficient water has been removed from the coal seam <b>15</b>, pure coal seam gas may be allowed to flow to the surface <b>14</b> through the annulus of the substantially vertical well bore <b>12</b> around the tubing string <b>82</b> and removed via piping attached to a well-head apparatus. At the surface, the methane is treated, compressed and pumped through a pipeline for use as a fuel in a conventional manner. The down hole pump <b>80</b> may be operated continuously or as needed to remove water drained from the coal seam <b>15</b> into the enlarged diameter cavity <b>22</b>.

FIGS. 4-7 illustrate substantially horizontal drainage patterns <b>50</b> for accessing the coal seam <b>15</b> or other subterranean zone in accordance with one embodiment of the present invention. In this embodiment, the drainage patterns comprise pinnate patterns that have a central diagonal with generally symmetrically arranged and appropriately spaced laterals extending from each side of the diagonal. The pinnate pattern approximates the pattern of veins in a leaf or the design of a feather in that it has similar, substantially parallel, auxiliary drainage bores arranged in substantially equal and parallel spacing or opposite sides of an axis. The pinnate drainage pattern with its central bore and generally symmetrically arranged and appropriately spaced auxiliary drainage bores on each side provides a uniform pattern for draining fluids from a coal seam or other subterranean formation. As described in more detail below, the pinnate pattern provides substantially uniform coverage of a square, other quadrilateral, or grid area and may be aligned with longwall mining panels for preparing the coal seam <b>15</b> for mining operations. It will be understood that other suitable drainage patterns may be used in accordance with the present invention.

The pinnate and other suitable drainage patterns drilled from the surface provide surface access to subterranean formations. The drainage pattern may be used to uniformly remove and/or insert fluids or otherwise manipulate a subterranean deposit. In non coal applications, the drainage pattern may be used initiating in-situ burns, “huff-puff” steam operations for heavy crude oil, and the removal of hydrocarbons from low porosity reservoirs.

FIG. 4 illustrates a pinnate drainage pattern <b>100</b> in accordance with one embodiment of the present invention. In this embodiment, the pinnate drainage pattern <b>100</b> provides access to a substantially square area <b>102</b> of a subterranean zone. A number of the pinnate patterns <b>60</b> may be used together to provide uniform access to a large subterranean region.

Referring to FIG. 4, the enlarged diameter cavity <b>20</b> defines a first corner of the area <b>102</b>. The pinnate pattern <b>100</b> includes a substantially horizontal main well bore <b>104</b> extending diagonally across the area <b>102</b> to a distant corner <b>106</b> of the area <b>102</b>. Preferably, the substantially vertical and articulated well bores <b>12</b> and <b>30</b> are positioned over the area <b>102</b> such that the diagonal bore <b>104</b> is drilled up the slope of the coal seam <b>15</b>. This will facilitate collection of water, gas from the area <b>102</b>. The diagonal bore <b>104</b> is drilled using the articulated drill string <b>40</b> and extends from the enlarged cavity <b>20</b> in alignment with the articulated well bore <b>30</b>.

A plurality of lateral well bores <b>110</b> extend from the opposites sides of diagonal bore <b>104</b> to a periphery <b>112</b> of the area <b>102</b>. The lateral bores <b>122</b> may mirror each other on opposite sides of the diagonal bore <b>104</b> or may be offset from each other along the diagonal bore <b>104</b>. Each of the lateral bores <b>110</b> includes a radius curving portion <b>114</b> coming off of the diagonal bore <b>104</b> and an elongated portion <b>116</b> formed after the curved portion <b>114</b> has reached a desired orientation. For uniform coverage of the square area <b>102</b>, pairs of lateral bores <b>110</b> are substantially evenly spaced on each side of the diagonal bore <b>104</b> and extend from the diagonal <b>64</b> at an angle of approximately 45 degrees. The lateral bores <b>110</b> shorten in length based on progression away from the enlarged diameter cavity <b>20</b> in order to facilitate drilling of the lateral bores <b>110</b>.

The pinnate drainage pattern <b>100</b> using a single diagonal bore <b>104</b> and five pairs of lateral bores <b>110</b> may drain a coal seam area of approximately 150 acres in size. Where a smaller area is to be drained, or where the coal seam has a different shape, such as a long, narrow shape or due to surface or subterranean topography, alternate pinnate drainage patterns may be employed by varying the angle of the lateral bores <b>110</b> to the diagonal bore <b>104</b> and the orientation of the lateral bores <b>110</b>. Alternatively, lateral bores <b>120</b> can be drilled from only one side of the diagonal bore <b>104</b> to form a one-half pinnate pattern.

The diagonal bore <b>104</b> and the lateral bores <b>110</b> are formed by drilling through the enlarged diameter cavity <b>20</b> using the articulated drill string <b>40</b> and appropriate horizontal drilling apparatus. During this operation, gamma ray logging tools and conventional measurement while drilling technologies may be employed to control the direction and orientation of the drill bit so as to retain the drainage pattern within the confines of the coal seam <b>15</b> and to maintain proper spacing and orientation of the diagonal and lateral bores <b>104</b> and <b>110</b>.

In a particular embodiment, the diagonal bore <b>104</b> is drilled with an incline at each of a plurality of lateral kick-off points <b>108</b>. After the diagonal <b>104</b> is complete, the articulated drill string <b>40</b> is backed up to each successive lateral point <b>108</b> from which a lateral bore <b>110</b> is drilled on each side of the diagonal <b>104</b>. It will be understood that the pinnate drainage pattern <b>100</b> may be otherwise suitably formed in accordance with the present invention.

FIG. 5 illustrates a pinnate drainage pattern <b>120</b> in accordance with another embodiment of the present invention. In this embodiment, the pinnate drainage pattern <b>120</b> drains a substantially rectangular area <b>122</b> of the coal seam <b>15</b>. The pinnate drainage pattern <b>120</b> includes a main diagonal bore <b>124</b> and a plurality of lateral bores <b>126</b> that are formed as described in connection with diagonal and lateral bores <b>104</b> and <b>110</b> of FIG. <b>4</b>. For the substantially rectangular area <b>122</b>, however, the lateral bores <b>126</b> on a first side of the diagonal <b>124</b> include a shallow angle while the lateral bores <b>126</b> on the opposite side of the diagonal <b>124</b> include a steeper angle to together provide uniform coverage of the area <b>12</b>.

FIG. 6 illustrates a quadrilateral pinnate drainage pattern <b>140</b> in accordance with another embodiment of the present invention. The quadrilateral drainage pattern <b>140</b> includes four discrete pinnate drainage patterns <b>100</b> each draining a quadrant of a region <b>142</b> covered by the pinnate drainage pattern <b>140</b>.

Each of the pinnate drainage patterns <b>100</b> includes a diagonal well bore <b>104</b> and a plurality of lateral well bores <b>110</b> extending from the diagonal well bore <b>104</b>. In the quadrilateral embodiment, each of the diagonal and lateral bores <b>104</b> and <b>110</b> are drilled from a common articulated well bore <b>141</b>. This allows tighter spacing of the surface production equipment, wider coverage of a drainage pattern and reduces drilling equipment and operations.

FIG. 7 illustrates the alignment of pinnate drainage patterns <b>100</b> with subterranean structures of a coal seam for degasifying and preparing the coal seam for mining operations in accordance with one embodiment of the present invention. In this embodiment, the coal seam <b>15</b> is mined using a longwall process. It will be understood that the present invention can be used to degassify coal seams for other types of mining operations.

Referring to FIG. 7, coal panels <b>150</b> extend longitudinally from a longwall <b>152</b>. In accordance with longwall mining practices, each panel <b>150</b> is subsequently mined from a distant end toward the longwall <b>152</b> and the mine roof allowed to cave and fracture into the opening behind the mining process. Prior to mining of the panels <b>150</b>, the pinnate drainage patterns <b>100</b> are drilled into the panels <b>150</b> from the surface to degasify the panels <b>150</b> well ahead of mining operations. Each of the pinnate drainage patterns <b>100</b> is aligned with the longwall <b>152</b> and panel <b>150</b> grid and covers portions of one or more panels <b>150</b>. In this way, a region of a mine can be degasified from the surface based on subterranean structures and constraints.

FIG. 8 is a flow diagram illustrating a method for preparing the coal seam <b>15</b> for mining operations in accordance with one embodiment of the present invention. In this embodiment, the method begins at step <b>160</b> in which areas to be drained and drainage patterns <b>50</b> for the areas are identified. Preferably, the areas are aligned with the grid of a mining plan for the region. Pinnate structures <b>100</b>, <b>120</b> and <b>140</b> may be used to provide optimized coverage for the region. It will be understood that other suitable patterns may be used to degasify the coal seam <b>15</b>.

Proceeding to step <b>162</b>, the substantially vertical well <b>12</b> is drilled from the surface <b>14</b> through the coal seam <b>15</b>. Next, at step <b>164</b>, down hole logging equipment is utilized to exactly identify the location of the coal seam in the substantially well bore <b>12</b>. At step <b>164</b>, the enlarged diameter cavity <b>22</b> is formed in the substantially vertical well bore <b>12</b> at the location of the coal seam <b>15</b>. As previously discussed, the enlarged diameter cavity <b>20</b> may be formed by under reaming and other conventional techniques.

Next, at step <b>166</b>, the articulated well bore <b>30</b> is drilled to intersect the enlarged diameter cavity <b>22</b>. At step <b>168</b>, the main diagonal bore <b>104</b> for the pinnate drainage pattern <b>100</b> is drilled through the articulated well bore <b>30</b> into the coal seam <b>15</b>. After formation of the main diagonal <b>104</b>, lateral bores <b>110</b> for the pinnate drainage pattern <b>100</b> are drilled at step <b>170</b>. As previously described, lateral kick-off points may be formed in the diagonal bore <b>104</b> during its formation to facilitate drilling of the lateral bores <b>110</b>.

At step <b>172</b>, the articulated well bore <b>30</b> is capped. Next, at step <b>174</b>, the enlarged diagonal cavity <b>22</b> is cleaned in preparation for installation of downhole production equipment. The enlarged diameter cavity <b>22</b> may be cleaned by pumping compressed air down the substantially vertical well bore <b>12</b> or other suitable techniques. At step <b>176</b>, production equipment is installed in the substantially vertical well bore <b>12</b>. The production equipment includes a sucker rod pump extending down into the cavity <b>22</b> for removing water from the coal seam <b>15</b>. The removal of water will drop the pressure of the coal seam and allow methane gas to diffuse and be produced up the annulus of the substantially vertical well bore <b>12</b>.

Proceeding to step <b>178</b>, water that drains from the drainage pattern <b>100</b> into the cavity <b>22</b> is pumped to the surface with the rod pumping unit. Water may be continuously or intermittently be pumped as needed to remove it from the cavity <b>22</b>. At step <b>180</b>, methane gas diffused from the coal seam <b>15</b> is continuously collected at the surface <b>14</b>. Next, at decisional step <b>182</b> it is determined whether the production of gas from the coal seam <b>15</b> is complete. In one embodiment, the production of gas may be complete after the cost of the collecting the gas exceeds the revenue generated by the well. In another embodiment, gas may continue to be produced from the well until a remaining level of gas in the coal seam <b>15</b> is below required levels for mining operations. If production of the gas is not complete, the No branch of decisional step <b>182</b> returns to steps <b>178</b> and <b>180</b> in which water and gas continue to be removed from the coal seam <b>15</b>. Upon completion of production, the Yes branch of decisional step <b>182</b> leads to step <b>184</b> in which the production equipment is removed.

Next, at decisional step <b>186</b>, it is determined whether the coal seam <b>15</b> is to be further prepared for mining operations. If the coal seam <b>15</b> is to be further prepared for mining operations, the Yes branch of decisional step <b>186</b> leads to step <b>188</b> in which water and other additives may be injected back into the coal seam <b>15</b> to rehydrate the coal seam in order to minimize dust, to improve the efficiency of mining, and to improve the mined product.

Step <b>188</b> and the No branch of decisional step <b>186</b> lead to step <b>190</b> in which the coal seam <b>15</b> is mined. The removal of the coal from the seam causes the mined roof to cave and fracture into the opening behind the mining process. The collapsed roof creates gob gas which may be collected at step <b>192</b> through the substantially vertical well bore <b>12</b>. Accordingly, additional drilling operations are not required to recover gob gas from a mined coal seam. Step <b>192</b> leads to the end of the process by which a coal seam is efficiently degasified from the surface. The method provides a symbiotic relationship with the mine to remove unwanted gas prior to mining and to rehydrate the coal prior to the mining process.

A well cavity pump comprises a well bore portion and a cavity positioned device. The well bore portion comprises an inlet for drawing and transferring well fluid contained within cavity <b>20</b> to a surface of vertical well bore <b>12</b>.

In this embodiment, the cavity positioning device is rotatably coupled to the well bore portion to provide rotational movement of the cavity positioning device ralative to the well bore portion. For example, a pin, shaft, or other suitable method or device (not explicitly shown) may be used to rotatably couple the cavity position device to the well bore portion to provide pivotal movement of the cavity positioning device about an axis relative to the well bore portion. Thus, the cavity positioning device may be coupled to the well bore portion between two ends of the cavity positioning device such that both ends may be rotatably manipulated relative to the well bore portion.

The cavity positioning device also comprises a counter balance portion to control a position of the ends relative to the well bore portion in a generally unsupported condition. For example, the cavity positioning device is generally cantilevered about the axis relative to the well bore portion. The counter balance portion is disposed along the cavity positioning device between the axis and the end such that a weight or mass of the counter balance portion counter balances the cavity positioning device during deployment and withdrawal of the well cavity pump relative to vertical well bore <b>12</b> and cavity <b>20</b>.

In operation, the cavity positioning device is deployed into vertical well bore <b>12</b> having the end and the counter balance portion positioned in a generally retracted condition, thereby disposing the end and the counter balance portion adjacent the well bore portion. As the well cavity pump travels downwardly within vertical well bore <b>12</b>, a length of the cavity positioning device generally prevents rotational movement of the cavity positioning device relative to the well bore portion. For example, the mass of the counter balance portion may cause the counter balance portion and the end to be generally supported by contact with a vertical wall of vertical well bore <b>12</b> as the well cavity pump travels downwardly within vertical well bore <b>12</b>.

As well cavity pump travels downwardly within vertical well bore <b>12</b>, the counter balance portion causes rotational or pivotal movement of the cavity positioning device relative to the well bore portion as the cavity positioning device transitions from vertical well bore <b>12</b> to cavity <b>20</b>. For example, as the cavity positioning device transitions from vertical well bore <b>12</b> to cavity <b>20</b>, the counter balance portion and the end become generally unsupported by the vertical wall of vertical well bore <b>12</b>. As the counter balance portion and the end become generally unsupported, the counter balance portion automatically causes rotational movement of the cavity positioning device relative to the well bore portion. For example, the counter balance portion generally causes the end to rotate or extend outwardly relative to vertical well bore <b>12</b>. Additionally, the end of the cavity positioning device extends or rotates outwardly relative to vertical well bore <b>12</b>.

The length of the cavity positioning device is configured such that the ends of the cavity positioning device become generally unsupported by vertical well bore <b>12</b> as the cavity positioning device transitions from vertical well bore <b>12</b> into cavity <b>20</b>, thereby allowing the counter balance portion to cause rotational movement of the end outwardly relative to the well bore portion and beyond an annulus portion of sump <b>22</b>. Thus, in operation, as the cavity positioning device transitions from vertical well bore <b>12</b> to cavity <b>20</b>, the counter balance portion causes the end to rotate or extend outwardly such that continued downward travel of the well cavity pump results in contact of the end with a horizontal wall of cavity <b>20</b>.

As downwardly travel of the well cavity pump continues, the contact of the end with the horizontal wall of cavity <b>20</b> causes further rotational movement of the cavity positioning device relative to the well bore portion. For example, contact between the end and the horizontal wall combined with downward travel of the well cavity pump causes the end to extend or rotate outwardly relative to vertical well bore <b>12</b> until the counter balance portion contacts a horizontal wall of cavity <b>20</b>. Once the counter balance portion and the end of the cavity positioning device become generally supported by the horizontal walls of cavity <b>20</b>, continued downwardly travel of the well cavity pump is substantially prevented, thereby positioning the inlet at a predefined location with cavity <b>20</b>.

Thus, the inlet may be located at various positions along the well bore portion such that the inlet is disposed at the predefined location within cavity <b>20</b> as the cavity positioning device bottoms out within cavity <b>20</b>. Therefore, the inlet may be accurately positioned within cavity <b>20</b> to substantially prevent drawing in debris or other material disposed within sump or rat hole <b>22</b> and to prevent gas interference caused by placement of the inlet <b>20</b> in the narrow well bore. Additionally, the inlet may be positioned within cavity <b>20</b> to maximize fluid withdrawal from cavity <b>20</b>.

In reverse operation, upward travel of the well cavity pump generally results in releasing contact between the counter balance portion and the end with horizontal walls, respectively. As the cavity positioning device becomes generally unsupported within cavity <b>20</b>, the mass of the cavity positioning device disposed between the end and the axis generally causes the cavity positioning device to rotate. Additionally, the counter balance portion cooperates with the mass of the cavity positioning device disposed between the end and the axis to generally align the cavity positioning device with vertical well bore <b>12</b>. Thus, the cavity positioning device automatically becomes aligned with vertical well bore <b>12</b> as the well cavity pump is withdrawn from cavity <b>20</b>. Additional upward travel of the well cavity pump then may be used to remove the cavity positioning device from cavity <b>20</b> and vertical well bore <b>12</b>.

Therefore, the present invention provides greater reliability than prior systems and methods by positively locating the inlet of the well cavity pump at a predefined location within cavity <b>20</b>. Additionally, the well cavity pump may be efficiently removed from cavity <b>20</b> without requiring additional unlocking or alignment tools to facilitate the withdrawal of the well cavity pump from cavity <b>20</b> and vertical well bore <b>12</b>.

Although the present invention has been described with several embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.